I've discovered in myself a tendency to say, "I need the Atonement to get to this spiritual point, and then I will be content." The problem with that is that it doesn't work. The moment I let myself be content and stop feeling the need for the Atonement, I quickly regress.
Repentance is an act, but it is also a lifestyle. I do not have the intelligence to be completely pure and good instantly, and if I did, I would be under enormous condemnation for not living up to that intelligence. Therefore, I constantly need the Atonement so that I can continue to grow. There are stepping stones for each of us--starting with temple worthiness, and moving forward through individual weaknesses and gaining specific gifts until we are perfect. But stepping stones are always taken one at a time.
I think the most accusatory way to describe perfectionism is a form of pride--a desire to be rid of the Atonement as soon as possible. Even the best of us need the Atonement to keep moving forward.